CN108445361B - System and method for measuring grounding resistance of direct current system for electric power - Google Patents

System and method for measuring grounding resistance of direct current system for electric power Download PDF

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CN108445361B
CN108445361B CN201810273005.XA CN201810273005A CN108445361B CN 108445361 B CN108445361 B CN 108445361B CN 201810273005 A CN201810273005 A CN 201810273005A CN 108445361 B CN108445361 B CN 108445361B
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CN108445361A (en
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黄海宏
刘妮妮
王海欣
叶超
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Hefei University of Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/025—Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters

Abstract

The invention discloses a system and a method for measuring the grounding resistance of a direct current system for electric power, which adopts a double bridge arm differential current method, R1、R2、R3、R4For detecting the resistance, K, inside the device1、K2、K3、K4Is a controllable switch, a first detection device connected in series, a controllable switch K1A second detection device and a controllable switch K connected in series between the positive bus and the ground2A third detection device and a controllable switch K which are connected between the negative bus and the ground in series3A fourth detection device and a controllable switch K which are connected between the positive bus and the ground in series4Connected between the negative bus and the ground through four switches K1、K2、K3、K4And (3) switching, namely deducing the insulation resistance value of the DC system to the ground by using the difference of leakage currents generated by alternately switching two groups of bridge arms. Compared with the prior art, the invention has the following advantages: and the double bridge arms are adopted to offset the zero drift of the direct current leakage current sensor, so that the accuracy of the differential current insulation monitoring method based on the unbalanced bridge can be improved, and the grounding resistance value of each branch can be accurately calculated.

Description

System and method for measuring grounding resistance of direct current system for electric power
Technical Field
The invention relates to the field of insulation monitoring of a direct-current power supply system, in particular to a system and a method for measuring ground resistance of a direct-current system for electric power.
Background
The direct current system of the power plant and the substation is an operation power supply of a control loop, a signal loop, a protection device, an automatic device and an automatic system in the power plant and the substation, and the reliability of the direct current system directly influences the running safety of the power system. Because the direct current system is widely distributed, the number of components is large, the environments are different, and the phenomena of insulation reduction and even one-point grounding can occur. Different from the connection between the positive output of a 48V direct current power supply for a communication base station and the ground, the output positive and negative buses of a direct current operating power supply for electric power are not grounded, so that one point is insulated and lowered or grounded, and no influence is caused on the direct current system and the direct current load work, but the direct current operating power supply for electric power must be found and eliminated in time, otherwise, when another point is insulated and lowered or grounded, the positive and negative buses of the direct current power supply output form a loop through the ground, and the false operation of a protection device can be caused, even a direct current breaker trips or a fuse fuses, so that a secondary loop loses the direct current operating power supply, and therefore, the direct current operating power supply.
Early dc systems of power plants and substations used bridge balancing to detect ground faults, as shown in fig. 1, where R is+And R-Respectively positive and negative DC bus resistance to ground, R is detection resistance inside the detection device, RJIs the resistance of the relay. When the insulation condition of the positive and negative buses is good, namely R+And R-When large, only a slight unbalance current flows through RJ. When the ground resistance of a certain level of the direct current bus is reduced to a certain threshold value, the bridge is out of balance, and current flows through RJWhen the relay acts, the insulation monitoring device sends out a grounding alarm signal. However, the bridge balancing technology cannot reflect the condition that the positive and negative bus insulation of the direct current system is equally reduced, and only the overall insulation state of the direct current system can be judged, and the fault branch location cannot be realized.
In order to meet the requirement of searching branches without power failure, from the end of the last 90 th century, a microcomputer direct-current grounding inspection instrument adopting a signal tracing method is widely applied to substations and power plants of 110kV or more. A milliampere-level Current Transformer (CT) is arranged on a direct current feed-out branch, as shown in figure 2. When the device detects that the insulation resistance of the positive bus and the negative bus to the ground is lower than a threshold value, the device injects a low-frequency alternating current signal into the positive bus, detects the amplitude and the phase of the low-frequency current of each branch circuit on the secondary side of the CT, and further calculates the insulation resistance of each branch circuit. When the device detects that the insulation resistance of the positive bus and the negative bus to the ground is lower than a threshold value, the device injects a low-frequency alternating current signal into the positive bus, detects the amplitude and the phase of the low-frequency current of each branch circuit on the secondary side of the CT, and further calculates the insulation resistance of each branch circuit.
The differential current detection method is a novel method, and detects the bus insulation condition by using an unbalanced bridge and realizes the detection of branch faults by combining a direct current leakage current sensor. Compared with the existing detection method, the method does not need to inject low-frequency signals into the system, does not interfere the direct current system, is irrelevant to the size of the distributed capacitance of the system, and has higher detection sensitivity.
In order to realize the insulation drop searching function of the direct current feed-out branch, the CT in fig. 2 is replaced by a non-contact direct current leakage current sensor, as shown in fig. 3, the magnitude and direction of the difference between the inflow current and the outflow current of any branch positive and negative wires can be detected.
At K+Or K-During the closing period, if no insulation resistance is reduced or no earth fault occurs, the current passes through the anode current I of the leakage current sensor+And a negative electrode current I-Equal in size and opposite in direction, i.e. I+＝I-And if the difference value between the two is zero, the output of the leakage sensor is 0.
K+Closed K-When the circuit is disconnected, if the insulation resistance of the negative electrode of the branch circuit is reduced or grounded, the grounding resistance of the negative electrode of the branch circuit is RZ-A loop is formed by the insulation detection resistor R and the positive bus through the ground, the negative pole of the branch circuit has leakage current, and the difference between the positive pole current and the negative pole current passing through the leakage current sensor is IZ-。K+Disconnect K-When the circuit is closed, if the insulation resistance of the anode of the branch circuit is reduced or grounded, the grounding resistance of the anode of the branch circuit is RZ+A loop is formed by the insulation detection resistor R and the negative bus through the ground, the leakage current exists at the anode of the branch circuit, and the difference between the anode current and the cathode current passing through the leakage current sensor is IZ+. And judging whether the branch has the ground fault and the polarity of the ground according to whether the direct current leakage sensor of each branch outputs 0 and the polarity of the output voltage. However, the calculation of the resistance value of the specific grounding needs to be analyzed and calculated according to the condition of the branch grounding point, and the specific condition can be distinguished according to single-branch grounding and multi-branch grounding.
FIG. 4 is a schematic diagram of a single-branch positive-negative-equal-grounding typical equivalent circuit for measuring insulation resistance by using single-bridge-arm differential current method, wherein R isfThe load resistor (is formed by air switches on the bus, when the corresponding air switch is closed, namely connected in parallel on the DC bus, it has no influence on the insulation detection, so it is equivalent to an equivalent resistor Rf)，R1、R2For detecting the resistance, K, inside the device+、K-Is a controllable switch, a first detection device connected in series, a controllable switch K+A second series-connected between the positive bus and the groundDetection device, controllable switch K-Connected between the negative bus and earth, RZ+And RZ-The resistance is divided into the insulation resistance of the positive pole and the negative pole in the branch circuit to the ground, namely the resistance to be detected. FIG. 5a is K+Closed K-Equivalent circuit at break, FIG. 5b is K+Disconnect K-An equivalent circuit when closed. Assuming a sense resistor R1、R2The resistance values of the two grounding circuits are all R, and the single-branch positive and negative grounding formula of the single-bridge arm differential flow method is as follows, wherein umThe voltage between the positive bus and the negative bus.
Figure BDA0001613005620000031
FIG. 6 is an equivalent circuit of negative grounding with multiple branches having grounding faults, wherein the positive pole is not grounded, i.e. the insulation resistance R of the positive pole of each branch to the earthZ1+～RZn+Is infinite, and K+Closed K-The equivalent circuit when the circuit is disconnected can calculate the insulation resistance R of each branch cathode to the groundZ1-～RZn-The specific numerical value of (1).
Figure BDA0001613005620000032
Similarly, when there are multiple branches with positive grounding and no negative grounding, it can be based on K1Disconnect K2Positive leakage current I measured at closureZ1+～IZn+Calculating the insulation resistance R of each branch anode to the groundZ1+～RZn+The specific numerical value of (1).
The existing differential current insulation monitoring method based on the unbalanced bridge has the advantages that insulation fault positioning and quantitative detection of a multi-branch direct current system can be realized, and the insulation condition of a branch can be judged by detecting the difference value of inflow current and outflow current of a branch loop by using a non-contact direct current leakage current sensor.
However, the method has the problem that in the differential current insulation monitoring process, when the measured leakage current value is small, the inherent null shift of the leakage current sensor can cause the error of the calculated insulation resistance to be large, and the insulation alarm is caused to be false.
Disclosure of Invention
The invention aims to solve the technical problem of how to eliminate the influence of zero drift of a direct current leakage current sensor on the accuracy of a differential current insulation monitoring method.
The invention solves the technical problems through the following technical scheme: a system for measuring the ground resistance of DC system for electric power features use of double bridge arm difference current method1、R2、R3、R4For detecting the resistance, K, inside the device1、K2、K3、K4Is a controllable switch, a first detection device connected in series, a controllable switch K1A second detection device and a controllable switch K connected in series between the positive bus and the ground2A third detection device and a controllable switch K which are connected between the negative bus and the ground in series3A fourth detection device and a controllable switch K which are connected between the positive bus and the ground in series4Connected between the negative bus and the ground, R in the case of a single branchfIs a load resistor connected in parallel on a DC busZ+And RZ-The resistance is divided into insulation resistance of the positive electrode and the negative electrode in the branch circuit to the ground, namely the resistance to be detected, and R is in the case of multiple branchesf1……RfnIs a load resistor connected in parallel on a DC busZ1+、RZ2+……RZn+And RZ1-、RZ2-……RZn-The resistance is divided into insulation resistance of the anode and the cathode of each branch in the branch circuit to the ground, namely resistance to be detected, wherein n is more than or equal to 2.
More specifically, the resistance R is set1、R2Is R, R3、R4Is (1/4) R.
The invention also provides a method for measuring by adopting the system for measuring the grounding resistance of the direct current system for electric power, and the measurement of the condition that the positive and negative of a single branch are grounded comprises the following steps:
1) make only K1Closed to obtain branch negative leakage current IZ1-；
Make only K3The closing process is carried out in a closed mode,get branch cathode leakage current IZ2-；
Make only K2Closed, divided into branch positive leakage current IZ1+；
Make only K4Closed, divided into branch positive leakage current IZ2+。
2) From the data obtained in 1), K1、K2And (3) alternately conducting to obtain a positive grounding resistance formula:
Figure BDA0001613005620000051
wherein u ismIs the voltage between the positive bus and the negative bus;
K3、K4and (3) alternately conducting to obtain a positive grounding resistance formula:
Figure BDA0001613005620000052
3) from equations (1) and (2):
Figure BDA0001613005620000053
in addition, make Δ I+＝IZ2+-IZ1+，ΔI-＝IZ2--IZ1-
Namely K2And K4When the two are respectively closed, the difference of the branch positive electrode leakage current is obtained as delta I+；K1And K3When the two are respectively closed, the difference of the branch cathode leakage current is obtained as delta I-。
Then there are:
Figure BDA0001613005620000054
the same principle is that:
Figure BDA0001613005620000055
simultaneously: delta I+RZ+＝ΔI-RZ-
Figure BDA0001613005620000061
Therefore, the method comprises the following steps:
Figure BDA0001613005620000062
4) deducing a formula for calculating the positive and negative grounding resistance values by using the leakage current difference according to the three steps:
Figure BDA0001613005620000063
the calculation steps of the multi-branch unipolar grounding are as follows:
1) taking two branches as negative grounding as an example, derivation is carried out:
definition IZ11-And IZ21-Are each K1When closed, flows through RZ1-And RZ2-The negative leakage current of (3); i isZ12-And IZ22-Are each K3When closed, flows through RZ1-And RZ2-negative leakage current.
K1Closing to obtain:
Figure BDA0001613005620000064
K3closing to obtain:
Figure BDA0001613005620000065
2) from equations (3) and (4):
Figure BDA0001613005620000071
another Delta I1＝IZ12--IZ11-，ΔI2＝IZ22--IZ21-
Namely,. DELTA.I1Is branch 1 at K1And K3Difference of leakage current obtained when the two are closed respectively; delta I2Is a branch2 at K1And K3The difference between the leakage currents obtained when the two are closed.
Then there are:
Figure BDA0001613005620000072
the same principle is that:
Figure BDA0001613005620000073
simultaneously: delta I1RZ1-＝ΔI2RZ2-
Figure BDA0001613005620000074
Therefore, the method comprises the following steps:
Figure BDA0001613005620000075
3) deducing a formula for calculating the negative grounding resistance values of the two branches by using the leakage current difference value according to the two steps:
Figure BDA0001613005620000076
4) the negative grounding condition of any branch is promoted by the formula (5):
Figure BDA0001613005620000077
wherein R isZ1-、RZ2-……RZn-The insulation resistance of the negative pole of each branch in the branch circuit to the ground, namely the resistance to be detected, is respectively, wherein n is more than or equal to 2.
The multi-branch positive grounding has the same principle as the multi-branch negative grounding.
Compared with the prior art, the invention has the following advantages: and the double bridge arms are adopted to offset the zero drift of the direct current leakage current sensor, so that the accuracy of the differential current insulation monitoring method based on the unbalanced bridge can be improved, and the grounding resistance value of each branch can be accurately calculated.
Drawings
FIG. 1 is a schematic diagram of an existing single bridge balancing method for detecting an insulation circuit;
FIG. 2 is a schematic diagram of a prior art signal tracking method;
FIG. 3 is a schematic diagram of the detection of the insulation condition of a feeding-out branch by a differential flow detection method in the prior art;
FIG. 4 is a schematic diagram of a single-branch circuit of the prior art single-bridge arm differential flow method;
FIG. 5a is K in FIG. 41When closed, the single bridge arm differential flow method is used for connecting the equivalent circuit with a single branch;
FIG. 5b is K in FIG. 42When closed, the single bridge arm differential flow method is used for connecting the equivalent circuit with a single branch;
FIG. 6 is K1When the circuit is closed, the single bridge arm differential flow method multi-branch grounding equivalent circuit is adopted;
FIG. 7 is a schematic diagram of a single branch circuit according to the double bridge arm differential method of the embodiment of the present invention;
FIG. 8a is K in FIG. 71When the bridge arm is closed, the double bridge arm difference flow method is adopted to connect the equivalent circuit of the single branch circuit to the ground;
FIG. 8b is K in FIG. 73When the bridge arm is closed, the double bridge arm difference flow method is adopted to connect the equivalent circuit of the single branch circuit to the ground;
FIG. 8c is K in FIG. 72When the bridge arm is closed, the double bridge arm difference flow method is adopted to connect the equivalent circuit of the single branch circuit to the ground;
FIG. 8d is K in FIG. 74When the bridge arm is closed, the double bridge arm difference flow method is adopted to connect the equivalent circuit of the single branch circuit to the ground;
FIG. 9 is a schematic diagram of a double bridge arm differential flow method multi-branch circuit according to an embodiment of the present invention;
FIG. 10a is K1When closed, the double bridge arm difference flow method multi-branch grounding equivalent circuit;
FIG. 10b is K3When closed, the double bridge arm difference flow method multi-branch grounding equivalent circuit is adopted.
Detailed Description
The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.
Please refer to fig. 7The system for measuring the grounding resistance of the direct current system for the electric power adopts a double bridge arm differential current method, and under the condition that the positive and negative of a single branch are grounded, R isfThe load resistance (the load resistance formed by the air switch on the bus, when the corresponding air switch is closed, namely connected in parallel on the DC bus, it has no influence on the insulation detection, so it is equivalent to an equivalent resistance Rf)，R1、R2、R3、R4For detecting the resistance, K, inside the device1、K2、K3、K4Is a controllable switch, a first detection device connected in series, a controllable switch K1A second detection device and a controllable switch K connected in series between the positive bus and the ground2A third detection device and a controllable switch K which are connected between the negative bus and the ground in series3A fourth detection device and a controllable switch K which are connected between the positive bus and the ground in series4Connected between the negative bus and earth, RZ+And RZ-The resistance is divided into the insulation resistance of the positive pole and the negative pole in the branch circuit to the ground, namely the resistance to be detected. And assume the above resistance R1、R2Is R, R3、R4Is (1/4) R.
Direct current system positive grounding resistance R for measuring electric power by adopting systemZ+And a negative ground resistance RZ-The method comprises the following steps:
the positive and negative of the single branch are grounded, and the equivalent circuit is shown in fig. 8a to 8 d:
1) make only K1Closing is shown in FIG. 8a, and the cathode leakage current I is divided into branchesZ1-；
Make only K3Closing as figure 8b, scoring the branch negative leakage current IZ2-；
Make only K2Closed as shown in FIG. 8c, and divided into branch positive leakage current IZ1+；
Make only K4Closed as shown in FIG. 8d, and divided into branch positive leakage current IZ2+。
2) From the data obtained in 1), K1、K2And (3) alternately conducting to obtain a positive grounding resistance formula:
Figure BDA0001613005620000101
wherein u ismThe voltage between the positive bus and the negative bus.
K3、K4And (3) alternately conducting to obtain a positive grounding resistance formula:
Figure BDA0001613005620000102
3) from equations (1) and (2):
Figure BDA0001613005620000103
in addition, make Δ I+＝IZ2+-IZ1+，ΔI-＝IZ2--IZ1-
Namely K2And K4When the two are respectively closed, the difference of the branch positive electrode leakage current is obtained as delta I+；K1And K3When the two are respectively closed, the difference of the branch cathode leakage current is obtained as delta I-；
Then there are:
Figure BDA0001613005620000104
the same principle is that:
Figure BDA0001613005620000105
simultaneously: delta I+RZ+＝ΔI-RZ-
Figure BDA0001613005620000106
Therefore, the method comprises the following steps:
Figure BDA0001613005620000107
4) the formula for calculating the positive and negative grounding resistance values by using the leakage current difference can be deduced according to the three steps:
Figure BDA0001613005620000111
the formula is an algorithm of single-branch positive and negative grounding, and the formula shows that the zero drift of the leakage current sensor can be eliminated by substituting the difference of the leakage currents measured by respectively switching two different bridge arms into calculation, so that the positive and negative ground insulation resistance values can be accurately calculated.
Referring to fig. 9, the system for measuring the ground resistance of the dc system for electric power according to the embodiment of the present invention adopts a double bridge arm differential current method, where R is the difference between two adjacent branchesf1……RfnIs a load resistance (R)f1……RfnAll are load resistors, the load resistors on a plurality of branches formed on the bus through the air switches are connected in parallel on the direct current bus when the corresponding air switches are closed, and have no influence on insulation detection), R1、R2、R3、R4For detecting the resistance, K, inside the device1、K2、K3、K4Is a controllable switch, a first detection device connected in series, a controllable switch K1A second detection device and a controllable switch K connected in series between the positive bus and the ground2A third detection device and a controllable switch K which are connected between the negative bus and the ground in series3A fourth detection device and a controllable switch K which are connected between the positive bus and the ground in series4Connected between the negative bus and earth, RZ1+、RZ2+……RZn+And RZ1-、RZ2-……RZn-The resistance is divided into insulation resistance of the anode and the cathode of each branch in the branch circuit to the ground, namely resistance to be detected, wherein n is more than or equal to 2. And assume the above resistance R1、R2Is R, R3、R4Is (1/4) R.
The multi-branch single-polarity grounding is as shown in fig. 10a and fig. 10 b:
1) taking two branches as negative grounding as an example, derivation is carried out:
definition IZ11-And IZ21-Are each K1When closed, flows through RZ1-And RZ2-The negative leakage current of (3); i isZ12-And IZ22-Are each K3When closed, flows through RZ1-And RZ2-The negative electrode leakage current of (1).
K1Closing to obtain:
Figure BDA0001613005620000121
K3closing to obtain:
Figure BDA0001613005620000122
2) from equations (3) and (4):
Figure BDA0001613005620000123
another Delta I1＝IZ12--IZ11-，ΔI2＝IZ22--IZ21-
Then there are:
Figure BDA0001613005620000124
the same principle is that:
Figure BDA0001613005620000125
simultaneously: delta I1RZ1-＝ΔI2RZ2-
Figure BDA0001613005620000126
Therefore, the method comprises the following steps:
Figure BDA0001613005620000127
namely,. DELTA.I1Is branch 1 at K1And K3Difference of leakage current obtained when the two are closed respectively; delta I2Is branch 2 at K1And K3The difference between the leakage currents obtained when the two are closed.
3) Deducing a formula for calculating the negative grounding resistance values of the two branches by using the leakage current difference value according to the two steps:
Figure BDA0001613005620000131
4) the negative grounding condition of any branch can be popularized by the formula (5):
Figure BDA0001613005620000132
wherein R isZ1-、RZ2-……RZn-The insulation resistance of the negative pole of each branch in the branch circuit to the ground, namely the resistance to be detected, is respectively, wherein n is more than or equal to 2.
The principle of the multi-branch positive grounding is the same as that of the multi-branch negative grounding, and no description is given. According to the formula, the grounding resistance value can be calculated as long as the difference between the leakage currents measured by respectively switching the two bridge arms with different resistance values is accurately obtained, and the zero drift of the direct current leakage sensor is offset at the moment.
The comparative experiment for measuring the grounding resistance by adopting the single bridge arm differential flow method in the prior art and the double bridge arm differential flow method in the application is as follows:
1. voltage u of positive and negative bus in circuitmIs provided by a 120V regulated power supply. The R resistance was 3.64k, and the 1/4R resistance was 0.91 k.
2. The resistors of 13k and 20k (actual values are respectively 12.94k and 19.96k) are respectively selected as the insulation resistors R of the branch anode to the groundZ+And insulation resistance of negative electrode to ground and RZ-With three branches in parallel: branch circuit 1, branch circuit 2, branch circuit 3, wherein branch circuit 2 and branch circuit 3 all are not earthed in this experiment, and only branch circuit 1 ground connection of the same way for simulate the condition of single branch circuit ground connection. The conditions of positive and negative grounding of a single branch are respectively simulated by using a single bridge arm differential flow method and a double bridge arm differential flow method in the prior art, and detection data are recorded in tables 1 and 2.
The single-bridge-arm differential flow method single-branch positive and negative equal grounding formula:
Figure BDA0001613005620000141
the double bridge arm difference flow method single branch positive and negative equal grounding formula:
Figure BDA0001613005620000142
TABLE 1
Figure BDA0001613005620000143
TABLE 2
Figure BDA0001613005620000144
3. The resistances of 13k, 20k, and 40k (actual values of 12.94k, 19.96k, and 39.7k, respectively) are used as the negative ground resistances of branch 1, branch 2, and branch 3. The conditions of multi-branch negative grounding are respectively simulated by using a single bridge arm differential flow method and a double bridge arm differential flow method, and detection data are recorded in tables 5 and 6.
The multi-branch negative grounding formula of the single-bridge arm differential flow method is as follows:
Figure BDA0001613005620000151
double bridge arm difference flow method multi-branch negative grounding formula:
Figure BDA0001613005620000152
TABLE 3
Figure BDA0001613005620000153
TABLE 4
Figure BDA0001613005620000161
Comparing the data in tables 1 and 2 and tables 3 and 4, it can be known that the double bridge arm differential method can basically eliminate the influence of the zero drift of the direct current leakage current sensor, and the detection is more accurate than the traditional single bridge arm differential method. In experiments, the measurement precision can be improved by increasing the bus voltage or properly reducing the resistance of the bridge arm. In practical engineering application, the selection of the bus detection resistance value needs to consider the power of the bus resistance and the maximum detection capability of the leakage sensor. In practice, the value of the bus detection resistance is carefully calculated according to the actual application, and the value has great influence on the detection precision.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

Claims (2)

1. The method for measuring the grounding resistance of the direct current system for electric power adopts a double bridge arm difference current method, R1、R2、R3、R4In order to detect devicesDetection resistance of section, K1、K2、K3、K4Is a controllable switch, a first detection device connected in series, a controllable switch K1A second detection device and a controllable switch K connected in series between the positive bus and the ground2A third detection device and a controllable switch K which are connected between the negative bus and the ground in series3A fourth detection device and a controllable switch K which are connected between the positive bus and the ground in series4Connected between the negative bus and the ground, R in the case of a single branchfIs a load resistor connected in parallel on a DC bus+And R-Respectively the insulation resistance of the positive bus and the negative bus in the circuit to the ground, namely the resistance to be detected, when the insulation condition of only a single branch circuit is reduced, R is definedZ+And RZ-Respectively the insulation resistance of the positive pole and the negative pole of the branch circuit to the ground, namely the resistance to be detected, and is characterized in that the resistance R is set1、R2Is R, R3、R4Is (1/4) R, and the measurement of the case where both the positive and negative of the single branch are grounded comprises the following steps:
1) make only K1Closed to obtain branch negative leakage current IZ1-；
Make only K3Closed to obtain branch negative leakage current IZ2-；
Make only K2Closed, divided into branch positive leakage current IZ1+；
Make only K4Closed, divided into branch positive leakage current IZ2+；
2) From the data obtained in 1), K1、K2And (3) alternately conducting to obtain a positive grounding resistance formula:
Figure FDA0002403985750000011
wherein u ismIs the voltage between the positive bus and the negative bus;
K3、K4and (3) alternately conducting to obtain a positive grounding resistance formula:
Figure FDA0002403985750000021
3) from equations (1) and (2):
Figure FDA0002403985750000022
in addition, make Δ I+＝IZ2+-IZ1+，ΔI-＝IZ2--IZ1-
Namely K2And K4When the two are respectively closed, the difference of the positive leakage current is obtained as delta I+；K1And K3When the two are respectively closed, the difference of the cathode leakage current is obtained as delta I-；
Then there are:
Figure FDA0002403985750000023
the same principle is that:
Figure FDA0002403985750000024
simultaneously: delta I+RZ+＝ΔI-RZ-
Figure FDA0002403985750000025
Therefore, the method comprises the following steps:
Figure FDA0002403985750000026
4) deducing a formula for calculating the positive and negative grounding resistance values by using the leakage current difference according to the three steps:
Figure FDA0002403985750000027
2. method for measuring by using system for measuring grounding resistance of direct current system for electric power, and method for measuring grounding resistance of direct current system for electric powerThe system of the resistor adopts a double bridge arm differential current method R1、R2、R3、R4For detecting the resistance, K, inside the device1、K2、K3、K4Is a controllable switch, a first detection device connected in series, a controllable switch K1A second detection device and a controllable switch K connected in series between the positive bus and the ground2A third detection device and a controllable switch K which are connected between the negative bus and the ground in series3A fourth detection device and a controllable switch K which are connected between the positive bus and the ground in series4Connected between the negative bus and the ground, R in the case of a single branchfIs a load resistor connected in parallel on a DC bus+And R-Respectively the insulation resistance of the positive bus and the negative bus in the circuit to the ground, namely the resistance to be detected, when the insulation condition of only a single branch circuit is reduced, R is definedZ+And RZ-Insulation resistance of the positive electrode and the negative electrode of the branch to the ground respectively, namely resistance to be detected, under the condition of multiple branches, Rf1……RfnIs a load resistor connected in parallel on a DC busZ1+、RZ2+……RZn+And RZ1-、RZ2-……RZn-Respectively the insulation resistance of the positive pole and the negative pole of each branch in the circuit to the ground, namely the resistance to be detected, wherein n is more than or equal to 2, and the method is characterized in that the resistance R is set1、R2Is R, R3、R4The resistance value of (1/4) R, the calculation steps of the multi-branch unipolar grounding are as follows:
1) taking two branches as negative grounding as an example, derivation is carried out:
definition IZ11-And IZ21-Are each K1When closed, flows through RZ1-And RZ2-The negative leakage current of (3); i isZ12-And IZ22-Are each K3When closed, flows through RZ1-And RZ2-The negative leakage current of (3);
K1closing to obtain:
Figure FDA0002403985750000031
K3closing to obtain:
Figure FDA0002403985750000032
2) from equations (3) and (4):
Figure FDA0002403985750000041
another Delta I1＝IZ12--IZ11-，ΔI2＝IZ22--IZ21-
Namely,. DELTA.I1Is branch 1 at K1And K3Difference of leakage current obtained when the two are closed respectively; delta I2Is branch 2 at K1And K3Difference of leakage current obtained when the two are closed respectively;
then there are:
Figure FDA0002403985750000042
the same principle is that:
Figure FDA0002403985750000043
simultaneously: delta I1RZ1-＝ΔI2RZ2-
Figure FDA0002403985750000044
Therefore, the method comprises the following steps:
Figure FDA0002403985750000045
3) deducing a formula for calculating the negative grounding resistance values of the two branches by using the leakage current difference value according to the two steps:
Figure FDA0002403985750000046
4) the negative grounding condition of any branch is promoted by the formula (5):
Figure FDA0002403985750000051
wherein R isZ1-、RZ2-……RZn-Respectively representing the insulation resistance of the negative pole of each branch in the circuit to the ground, namely the resistance to be detected, wherein n is more than or equal to 2;
the multi-branch positive grounding has the same principle as the multi-branch negative grounding.
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